x86/HVM: 32-bit IN result must be zero-extended to 64 bits

Just like for all other operations with 32-bit operand size.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -221,13 +221,15 @@ int handle_mmio_with_translation(unsigne
     return handle_mmio();
 }
 
-int handle_pio(uint16_t port, int size, int dir)
+int handle_pio(uint16_t port, unsigned int size, int dir)
 {
     struct vcpu *curr = current;
     struct hvm_vcpu_io *vio = &curr->arch.hvm_vcpu.hvm_io;
     unsigned long data, reps = 1;
     int rc;
 
+    ASSERT((size - 1) < 4 && size != 3);
+
     if ( dir == IOREQ_WRITE )
         data = guest_cpu_user_regs()->eax;
 
@@ -237,7 +239,12 @@ int handle_pio(uint16_t port, int size, 
     {
     case X86EMUL_OKAY:
         if ( dir == IOREQ_READ )
-            memcpy(&guest_cpu_user_regs()->eax, &data, vio->io_size);
+        {
+            if ( size == 4 ) /* Needs zero extension. */
+                guest_cpu_user_regs()->eax = (uint32_t)data;
+            else
+                memcpy(&guest_cpu_user_regs()->eax, &data, size);
+        }
         break;
     case X86EMUL_RETRY:
         if ( vio->io_state != HVMIO_awaiting_completion )
--- a/xen/include/asm-x86/hvm/io.h
+++ b/xen/include/asm-x86/hvm/io.h
@@ -119,7 +119,7 @@ void send_timeoffset_req(unsigned long t
 void send_invalidate_req(void);
 int handle_mmio(void);
 int handle_mmio_with_translation(unsigned long gva, unsigned long gpfn);
-int handle_pio(uint16_t port, int size, int dir);
+int handle_pio(uint16_t port, unsigned int size, int dir);
 void hvm_interrupt_post(struct vcpu *v, int vector, int type);
 void hvm_io_assist(void);
 void hvm_dpci_eoi(struct domain *d, unsigned int guest_irq,